1. Field of the Invention
The field of the present invention is hydraulic pressure control systems having a hydraulic pressure control valve including a housing with an output port connected to hydraulically operated devices, an input port communicating with a hydraulic pressure supply source and a release port communicating with a reservoir, a spool slidably received in the housing for axial movement between a rear position in which it permits communication between the output port and the release port and a front position in which it permits the communication between the input port and the output port, a reaction chamber defined in the housing to exhibit a hydraulic pressure for biasing the spool rearwardly and connected to the output port, and an input pressure working chamber defined in the housing to exhibit a hydraulic pressure for biasing the spool forwardly.
2. Description of the Prior Art
Such a hydraulic pressure control system is conventionally known, for example, from Japanese Patent Application Laid-open No. 116346/87.
In such a hydraulic pressure control system, the output port is connected to the reaction chamber. When the hydraulic pressure supply source is put into communication with the output port in response to the advancing movement of the spool according to a braking operation, a hydraulic pressure from the hydraulic pressure supply source is immediately applied to the reaction chamber so that the output hydraulic pressure from the hydraulic pressure control valve is increased in proportion to the amount of braking operation from the initial stage of the braking operation. In the system, however, the hydraulic braking pressure is relatively small at the initial stage of the braking operation and in some cases, the braking operation of a brake device such as the hydraulically operated device may not be smooth.